Simultaneous detection of cryoglobulins and cryofibrinogens in human plasma is confirmed in over 600 clinical chemistry specimens. Results are similar in carefully prepared serum and citrated plasma. The latter method is technically superior and easier. Positive assays are confirmed by electrophoresis of plasma supernatant kept at 4 degrees C at all times (control) and plasma supernatant rewarmed to 37 degrees C after being precipitated at 4 degrees C (test). We find 30 degrees of patients with Lupus erythematosus, rheumatoid arthritis, myelomas, dysproteinemias, clinically significant urticarias to be positive for cryoglobulins. In our asymptomatic (control) population, we find 8 percent positive specimens. Cryofibrinogens are exceedingly rare.